remove special nan handling from x86 sqrt asm

a double precision nan, when converted to extended (80-bit) precision,
will never end in 0x400, since the corresponding bits do not exist in
the original double precision value. thus there's no need to waste
time and code size on this check.

src/math/i386/sqrt.s

@@ -10,9 +10,6 @@ sqrt:	fldl 4(%esp)
 	and $0x7ff,%ecx
 	cmp $0x400,%ecx
 	jnz 1f
-	mov 8(%esp),%cx
-	inc %cx
-	jo 1f
 	and $0x200,%eax
 	sub $0x100,%eax
 	sub %eax,(%esp)